Commercially available polymers having hydrophilic properties are of great utility, particularly in areas such as such as improved resistance to the adsorption of oils and proteins, biocompatibility, reduced static charge build-up, and improved wettability to materials such as glues, inks, paints and water. Applications for such polymers include water filtration membranes and biocompatible medical devices and articles.
In many applications, polymers having optimal mechanical, thermal and chemical stability are hydrophobic. Because a hydrophobic polymer or article is difficult to wet and is susceptible to fouling, the article can be coated with a hydrophilic species, either covalently or by adsorption, or otherwise treated to provide hydrophilic properties. Articles coated in this manner require additional processing steps, which increase the manufacturing cost of the article. Where the article has membrane applications, the coating may reduce pore size and thus reduced permeability. In addition, coatings not covalently attached may suffer from insufficient chemical or mechanical stability. Even if the coatings are covalently attached coatings, such as those prepared by surface graft polymerization, residual reactants resulting from the reaction for covalent attachment require extraction prior to use.
Moreover, surface coverage of graft-polymerized coatings is difficult to control. Coating of the membrane separation surface does not prevent fouling of internal pore channels.
The development of graft copolymers afforded a possibility to overcome many of the disadvantages discussed above. A “graft copolymer” is produced by covalently bonding a species to be grafted, also referred to as a comonomer, to a parent polymer which provides the backbone in the graft copolymer. Graft copolymers derived from a parent polymer are typically used for providing a material with specific properties while retaining desirable properties of the parent polymer.
The synthesis of graft copolymers is most commonly accomplished via free-radical reactions initiated by exposing the polymer to ionizing radiation and/or a free-radical initiator in the presence of the comonomer. Free radical syntheses in this manner, however, can be an uncontrolled process. Numerous radicals are present not only on the polymer but also on the comonomer, which can undergo free-radical homopolymerization resulting in a mixture of homopolymers and graft copolymers. Thus, a significant disadvantage of these free-radical techniques is that the product is typically a mixture of graft copolymer and homopolymer. Moreover, polymer backbone degradation and/or crosslinking can occur as a result of uncontrolled free-radical production.
Thus, there exists a need to prepare graft copolymers via a facile, inexpensive process.